Stormwater runoff collected from roof areas and paved areas were historically directed into municipal stormwater drainage systems and released into a local body of water. However, regulatory changes and good practice now mandate that stormwater runoff must be collected and directed to local soil where it can replenish groundwater supplies.
The traditional construction of stormwater handling systems has been concrete tanks or infiltration trenches filled with large gravel or crushed stone with perforated pipes running therethrough. Such stone filled trench systems are non-economical and/or inefficient since the stone occupies a substantial volume, limiting the ability of the system to handle large surge volumes associated with heavy storms. Both the stone and the perforated pipe are also susceptible to clogging by particles or debris carried by water.
Molded plastic chamber structures were introduced to the market to take the place of concrete structures for handling stormwater. U.S. Pat. No. 5,087,151 to Robert J. DiTullio, the disclosure of which is hereby incorporated by reference, is an early patent in the field which discloses a drainage and leaching field system comprising vacuum-molded polyethylene chambers that are designed to be connected and locked together in an end-to-end fashion to provide a water handling system.
Stormwater chambers typically have a corrugated arch-shaped cross-section and are relatively long with open bottoms for dispersing water to the ground. The chambers are typically buried within crushed stone aggregate or other water permeable granular medium that typically has 20-40 percent or more void space. The chambers serve as water reservoirs in a system that includes both the chambers and surrounding crushed stone. The crushed stone is located beneath, around, and above the chambers and acts in combination with the chambers to provide paths for water to percolate into the soil, and also provides a surrounding structure that bears the load of any overlying materials and vehicles. The chambers will usually be laid on a crushed stone bed side-by-side in parallel rows, then covered with additional crushed stone to create large drainage systems. End portions of the chambers may be connected to a catch basin, typically through a pipe network, in order to efficiently distribute high velocity stormwater. Examples of such systems are illustrated in U.S. Pat. Nos. 7,226,241 and 8,425,148 to Robert J. DiTullio, the disclosures of which are also incorporated by reference.
The use of molded plastic chamber structures has grown substantially since their initial introduction to the market, and have replaced the use of concrete structures in many applications. Molded plastic chamber structures provide a number of distinct advantages over traditional concrete tanks or stone-filled trench systems. For example, concrete tanks are extremely heavy requiring heavy construction equipment to put them in place. Stone-filled trench systems are expensive and inefficient since the stone occupies a substantial volume, limiting the ability of the system to handle large surge volumes of water associated with heavy storms.
More recently, manufacturers have begun to offer taller chambers which offer larger volume and storage capacity. Examples of recently introduced large capacity chambers include the Cultec® 902HD®, Contech® Chambermaxx®, Stormtech® MC-3500 and 4500, Prinsco® HS180, and Lane SK180.
A design consideration associated with larger size stormwater chambers is that such structures may experience greater load stress than smaller chambers. A chamber should have a load bearing strength capable of bearing the load of the overlaying crushed stone and paving, and loads corresponding to use of construction equipment and vehicular traffic over the location of the buried chamber. Therefore, use of sub-corrugations molded into the corrugations to improve the strength of larger size plastic stormwater chambers has been proposed. U.S. Pat. No. 8,491,224 describes a chamber for stormwater runoff with sub-corrugation features on corrugation peaks and/or corrugation valleys. U.S. Pat. No. 8,672,583 similarly describes a plastic stormwater chamber with sub-corrugations that run along peak corrugations or valley corrugations. U.S. Pat. No. 8,672,583 defines sub-corrugations as “smaller or secondary corrugations which are superimposed on the corrugations.” (U.S. Pat. No. 8,672,583 at Col. 3, lines 26-27; see also Col. 6, lines 53-57).
A commercially acceptable product is required to fit on a standard size pallet and to be stackable such that a commercially acceptable quantity of product can be shipped on each pallet. Typically, a pallet may not exceed 40×48 inches in size and/or 84 inches in height, although the exact size is determined by each carrier. Although shipping costs are typically based on weight, many carriers also offer a per-pallet pricing where the shipper pays fixed amount per pallet no matter what the freight commodity or the freight class. It is commercially desirable to fit as much product on a pallet as possible, in order to minimize shipping costs. Thus products are designed in order to be fitted on and shipped with the maximum quantity of product on a pallet. In the case of plastic stormwater chambers this means that desirably six or more large size chambers can fit on a pallet so that the value of product shipped is commercially proportionate to the shipping cost. A plastic stormwater storage chamber designed so that four or less large size chambers fit on a pallet would not provide a value of product shipped that is commercially proportionate to the shipping cost.
Identically-formed chambers with corrugations can be readily stacked as they nest together one on top of the other sufficiently closely that the quantity of product on a pallet is commercially acceptable. Chambers with sub-corrugations on the corrugations nest together and can be stacked in a way that permits a commercially acceptable quantity of product to be loaded on a pallet. But chambers that do not nest together will not permit packing a sufficient number of chambers on a pallet.
One example of chambers that have heretofore been considered undesirable because of the inability to nest them together for packing are stormwater chambers with reinforcing ribs or fins instead of subcorrugations. Ribs and fins are relatively narrow plastic structures used for strengthening. A properly-sized rib or fin can provide greater strengthening effect and stiffness relative to a sub-corrugation. However, the increase in strength provided has heretofore been at the loss in commercial acceptability in packaging, particularly with respect to larger size chambers. The use of reinforcing ribs or fins or other increases in wall thickness prevents the chambers from nesting together in a stack. The stacking and other problems associated with use of ribs or fins is well recognized in the art. (See e.g. U.S. Pat. No. 8,672,583 at Col. 2, lines 6-12, and 46-52, and Col. 4, lines 4-9.) As such, ribs and fins are generally considered by persons of ordinary skill in the art to be a distinctly different feature than a sub-corrugation. See e.g. U.S. Pat. No. 8,672,583 at col. 6, lines 64-67.
Therefore, there continues to be a need in the stormwater management field for larger size chambers that have strengthening elements that have both the strength of ribbing, and the stackability of sub-corrugations. The desired chamber would be both stronger than existing design approaches, and also be adapted for efficient and cost effective distribution and transportation of such chambers.